1. Field of the Invention
The present invention relates to a loadlock apparatus having a loadlock chamber and an elevator extending into the loadlock chamber. More particularly, the present invention relates to sealing structure that creates a seal between a drive shaft of the elevator and the loadlock chamber into which the drive shaft extends.
2. Description of the Related Art
In general, in the fabricating of a semiconductor device, a wafer is passed through a loadlock chamber before being introduced into a process chamber in which the wafer is processed in a vacuum. Such a loadlock chamber receives the non-processed wafer from the outside under atmospheric pressure. The wafer is then loaded from the loadlock camber into the process chamber under the same vacuum atmosphere as the process chamber. The processed wafer is returned to the loadlock chamber and is then transferred from there for subsequent processing.
FIG. 1 shows such loadlock chamber 10, and an elevator 20 provided for use in transferring wafers to and from the loadlock chamber 10. The elevator 20 is configured to store numerous wafers and to raise and lower these wafers within the loadlock chamber 10. More specifically, the elevator 20 includes a wafer cassette 21, and an elevator drive shaft 22 connected to a lower portion of the cassette 21. The cassette may have 29 slots for accommodating 29 wafers, respectively. The elevator 20 also includes a specific driving unit (not shown in the drawings) for moving the elevator drive shaft 22 axially over a stroke which enables the cassette to, in turn, move between a position at which slot number 1 of the cassette is located at a loading/unloading position and a position at which slot number 29 of the cassette is located at the loading/unloading position.
Meanwhile, maintaining the air-tightness of the loadlock chamber 10 is extremely important because the loadlock chamber 10 is temporarily placed in open communication with the process chamber when a wafer is transferred therebetween. In particular, the most difficult portion of the loadlock chamber 10 to keep sealed is that portion where the elevator drive shaft 22 extends through the bottom of the loadlock chamber 10. Specifically, as the elevator shaft 22 is raised, air from the outside may flow into the loadlock chamber 10 along with that portion of the elevator drive shaft 22 entering the loadlock chamber 10. At present, this portion of the loadlock apparatus is provided with a dynamic seal to prevent such an inflow of air, i.e., in an attempt to maintain the air-tightness of the loadlock chamber 10 during the operation of the elevator 20.
FIG. 2 shows a prior art dynamic sealing structure 30 for providing a seal with an elevator drive shaft 22 at the bottom of a loadlock chamber. The sealing structure 30 is largely constructed of a base 31, a fixed cap 32, an elevator guide 33, a mounting member 34, a seal 35 and a seal cover 36. The base 31 covers and is fastened along the circumference of a hole in a bottom wall of the loadlock chamber. The elevator guide 33 is made of Teflon® and is disposed on an upper part of the base 31 at the center of the base 31. The mounting member 34 is made of metal and is integrated with the elevator guide 33 at an outer circumferential portion of the elevator guide 33. The fixed cap 32, whose interior is open in a downward direction, covers an upper part of the mounting member 34 and is secured to the base 31 by bolts to thereby secure the elevator guide 33 to the base 31.
Furthermore, the seal 35 is disposed on an upper end of the elevator guide 33. The seal 35 is covered with the seal cover 36. A lower end part of the seal cover 36 is interposed between the elevator guide 33 and the inner circumferential portion of the fixed cap 32, whereby the seal cover 36 is held in place. On the other hand, an outer circumferential part of the seal cover 36 is disposed on an upper portion of the fixed cap 32. This outer circumferential part of the seal cover 36 is fastened together with the fixed cap 32 to the mounting member 34 by bolts. This assembly thus constitutes a solid structural combination and yet allows for the necessary movement between respective components.
However, a leak check executed after the sealing structure 30 and the elevator shaft 22 are assembled and are integrated with the loadlock chamber 10 often reveals a leak. The leak is attributed to the tolerances which allow the fixed cap 32 to be bolted to the base 31 with some degree of flexibility, and to the fact that the elevator drive shaft 22 is not always inserted into the loadlock chamber 10 uniformly (see FIGS. 3 and 4). Furthermore, when the elevator drive shaft 22 is driven in this state, the friction between the seal 35 and the elevator drive shaft 22 causes unequal wear in the seal 35, whereby the useful life of the seal 35 is shortened (FIG. 4).